Need help with strange scaling behavior on my torso model; following a blender video
You have a different number of loop cuts than the example - were you embellishing the design, or had you made some errors in following the example?  From my own experiences, making errors and then correcting them during a tutorial led to some weird results and it was a while before I learnt to remove duplicates.

To check your theory about double vertices, select your entire mesh (A followed by A again should do the trick from the view in the images) and then select remove duplicates from your left hand menu. Off the top of my head, I can't remember if it is T or N to display this menu from the view that you have in your images - one will bring up the right properties menu and the other will bring up the left menu options. 

Are you also trying to scale along the right axes? S-Y will ensure it is locked on the y-axis as noted in the video. Selecting Shift-Y instead of Y will result in the scaling happening along the X- and Z-axes. Can't judge from your static screen shots.